1. Field of the Invention
The present invention relates to a molding method and apparatus therefor, and more particularly to a method of pressure molding casting and an apparatus therefor in which sufficient force is applied to a molten material in a mold by a compressed gas to force the material into the mold.
2. Description of Related Art
In conventional pressure molding methods, a molten material is fed into a casting cavity of a mold made of particulate refractory through a pouring gate communicating the casting cavity to the exterior of the mold. Thereafter, a part surrounding the pouring gate of the mold is covered by a cover member formed with a peripheral flange to which a flexible sealing member is attached to form therein a pressure chamber in communication with a pressure source so as to conceal the pouring gate completely. Compressed air is then supplied into the pressure chamber of the cover member to force the molten material to stay in the pouring gate. A molding device embodying such a pressure molding method is known from, for example, Japanese Utility Model Application No. 61-131900 entitled "Full Mold Casting Device" filed on Aug. 28, 1986 and laid open as Japanese Unexamined Utility Model Publication No. 63-41352 on Mar. 18, 1988.
The molding device as described in the above publication deforms a flexible sealed member to conform to an opening of the pouring gate so as thereby to forcibly press the molten material in the pouring gate. The molding device, however, has a problem in that the flexible sealing member is damaged by heat transmitted thereto from the molten material. Accordingly, compressed air in the pressure chamber of the cover member escapes into the mold of particulate refractory. Thus, sure pressurization of the molten material in the pouring gate, and hence in the casting cavity of the mold, is not always provided. Accordingly, a product cast by such a molding device blow holes and/or has a structure with a non-uniform density.